The forum’s cleanse protocol recommends chia seeds over psyllium husk, so I think they’re the safest bet. Since the seeds are hydrophilic, they absorb water into a coating around them, so they shouldn’t be able to scratch at your intestines, which is important if you have leaky gut. I’m not sure how gas-producing you’ll find them. If you do choose to use them to see if they work for you, make sure you drink a lot of water with them, as some people I know have reported constipation from using them. I think that is largely due to inadequate water intake.
As for black or white chia, I don’t think it makes any difference. I’d say buy the cheaper one, or maybe compare nutrient content on the packaging to see if one seems more beneficial.